The present invention relates to anchoring means for mine roof structures and the like, and more specifically to anchor systems of the type utilizing both a mechanical expansion anchor and a hardened resin to anchor the end of a mine roof bolt or threaded rebar in a drill hole.
Among the most common means of supporting the roofs and stabilizing and reinforcing rock strata in underground mines is an elongated rod, such as a bolt or rebar, having one end anchored firmly in a drill hole in the rock formation and the other end extending outside the opening to hold a bearing plate in tight engagement with the portion of the roof surrounding the bore hole opening. Anchor means for the elongated rods include mechanical expansion anchors wherein a tapered nut is advanced down the threaded end of the rod to expand a shell into gripping engagement with the walls of the bore hole, resin grouting means, and combinations of the two, among others.
In combination anchors, such as disclosed, for example, in U.S. Pat. Nos. 4,162,133, 3,324,663 and 2,829,502, a two-compartment resin cartridge is inserted in the drill hole ahead of the expansion anchor, the tapered nut of which is threaded on the end of the bolt or rebar. When the resin cartridge is engaged against the blind end of the hole, continued advancement and rotation of the bolt and anchor in one direction or the other, depending on the design of the unit, breaks the cartridge and mixes the two initially isolated components to permit the resin to harden. The bolt is then rotated to cause the tapered nut to expand the shell into engagement with the drill hole wall, the bolt is tensioned to the desired degree, and is anchored by the combined holding power of the expansion anchor and the hardened resin. While a number of such combination anchors have been provided, it is sometimes difficult to insure that the mechanical anchor goes into expansion at the desired time and/or the design requires custom casting or machining of the expansion anchor elements.
It is a principal object of the present invention to provide a combination mechanical expansion and resin grouted mine roof bolt anchor which utilizes tapered nuts and expansion shells of andard, commercially available design.
Another object is to provide a combination mechanical-resin bolt anchor system having novel and improved means for rotationally coupling the bolt and expansion anchor as the resin cartridge is broken and its contents mixed, and thereafter causing the shell to expand in the proper manner.
A further object is to provide a mechanical expansion anchor having combined structure which facilitates both the breaking of a resin cartridge and expansion of the shell at the desired point in the installation cycle.
Other objects will in part be obvious and will in part appear hereinafter.